Chemist Jacqueline Schwark (left) and Dr. Paul Hochgesang examine the surfaces of seals made from the new material for irregularities. (Photo: Freudenberg Sealing Technologies)
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Freudenberg Sealing Technologies, Weinheim, has developed a new EPDM material specifically for the requirements of the aerospace industry. Thanks to the new material, hydraulic seals also work leak-free at great heights and at low temperatures.
The new material 80 EPDM 426288 securely seals hydraulic systems that work at temperatures as low as -65 ° C – a breakthrough in EPDM formulations. Instead of large quantities of plasticizers, the scientists at Freudenberg Sealing Technologies use a special polymer to manufacture the new material.
The material meets the strict requirements of the AMS7361 specification for improved low-temperature behavior in hydraulic systems in commercial aircraft. Both in laboratory tests and in use, 80 EPDM 426288 shows good sealing behavior at low temperatures after it has been exposed to intensive loads from liquids, pressures and extreme temperatures. The material can be made to resist sunlight, ozone and chemical degradation, effectively seal off phosphate ester hydraulic fluids and other fluids, and function at temperatures up to 150 ° C.
Challenge for developers
In commercial aircraft – which fly at altitudes of almost 13,000 m at up to 926 km / h – standard EPDM materials are used to seal critical hydraulic systems, for example in the landing gear. At such altitudes and at such speeds, the frictional heat generated when the aircraft moves through the air keeps the temperature of the hydraulic system in a range in which conventional EPDM components retain their full functionality.
But commercial aircraft are not the only aircraft flying in the sky today. Turboprop transport machines and unmanned aerial vehicles, so-called drones, are also on the move there. Drones in particular are now used as standard when it comes to collecting data and delivering goods in areas such as medicine, environmental protection, surveying, film and photography, law enforcement and disaster relief.
However, drones are also a challenge for aerospace engineers: The speeds at which they fly – typically 160 km / h or less – combined with flying at the same or even greater altitudes as commercial aircraft reduce air friction and heat the outside of the aircraft. As a result, they have to endure very cold temperatures for long periods of time, followed by an abrupt change in temperature upon landing. The same goes for cargo planes and other slow-flying aircraft.
Standard EPDM materials become brittle and crack after prolonged use at very low temperatures. These cracks can cause fluid leaks in critical systems such as hydraulic brake lines. So engineers in the aerospace industry began looking for a solution to such leakage problems. At the same time, new hydraulic fluids came onto the market, which also made it necessary to develop and evaluate new material recipes.
Success factor international research team
Under the direction of Dr. Paul Hochgesang, who works in materials research in the Freudenberg Sealing Technologies laboratories in Plymouth (USA), several new EPDM formulations have been developed. The team used modern monomer and polymer technologies to achieve a better balance between behavior at high and low temperatures. These formulas showed very good results with regard to the material standards required in the aerospace industry. However, the materials could not pass long cold tests – they lost strength and became brittle.
“We mixed a variety of ingredients, including plasticizers, fillers, and heat stabilizers. Nevertheless, we were still unable to achieve the temperature gradient that our customers needed, ”comments Hochgesang. “At that moment, our company’s material and procurement experts in Germany and Japan came into play.”
They introduced Hochgesang, a new, largely unknown industrial polymer. In conjunction with a new EPDM formulation, the resulting material not only met the cold temperatures required by customers in the aerospace industry, but even exceeded them. The final development of 80 EPDM 426288 then took less than six months.
“This is an excellent example of the international collaboration between Freudenberg scientists. We can be successful by pooling the knowledge and skills of colleagues from all over the world, ”continues Hochgesang. “We have already overcome many of our toughest challenges this way.”
Seals and components made from 80 EPDM 426288 have already been manufactured in Freudenberg Sealing Technologies plants in North America and Europe and have been tested by several major manufacturers and system suppliers in the aerospace industry. Following the positive feedback from customers, the series production of O-rings for the aerospace industry made of the new EPDM material has now started.
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